JP2004103546A - Positive active material composite particle, electrode using the same, and lithium secondary battery - Google Patents
Positive active material composite particle, electrode using the same, and lithium secondary battery Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、リチウム二次電池に用いられる正極活物質複合化粒子、並びに該複合化粒子を用いた電極及びリチウム二次電池に関するものである。
【0002】
【従来の技術】
リチウム二次電池は、エネルギー密度及び出力密度等に優れ、小型化・軽量化できるため、ノート型パソコン、携帯電話及びハンディビデオカメラ等の携帯機器の電源として急激な伸びを示している。また、電気自動車や電力のロードレベリング等の電源としても注目されている。
【0003】
リチウム二次電池に用いられる正極は、通常、集電体、並びにその表面に形成される正極活物質、導電剤及び結着剤を含有する正極活物質層から構成されている。正極活物質としては、リチウム・マンガン複合酸化物、リチウム・コバルト複合酸化物又はリチウム・ニッケル複合酸化物等のリチウムとマンガン、コバルト又はニッケル等の遷移金属との複合酸化物が高性能の電池特性が得られるため注目されている。これらのリチウム系複合酸化物を用いたリチウム二次電池は、高い電圧を得ることが可能であり、高い出力が得られるという利点を有する。現在、複合酸化物の安定性、電池の高容量化、高温時での電池特性の改良を目的とした研究が活発に行われている。
【0004】
特開平11−154515号公報には、リチウム系複合酸化物、この複合酸化物の各粒子表面を被覆する第1の導電剤及び複合酸化物の各粒子間に介在し比表面積が第1の導電剤よりも小さい第2の導電剤を含む正極活物質が記載されている。
また、特開2000−123876号公報には、リチウム系複合酸化物、導電剤及び結着剤を混ぜ合わせながら、加圧力及び剪断応力を加えてリチウム系複合酸化物の表面に導電剤と結着剤とを付着させて複合化処理する正極材料の製造方法が記載されている。
【0005】
しかしながら、本発明者等の検討によると、これらのリチウム系複合酸化物、特にリチウム・ニッケル系複合酸化物を用いたリチウム二次電池は、高容量を有する一方で、低温雰囲気下での出力が低下するという問題を内在することが判明した。
また、二次電池では、常にサイクル寿命が重要視されている。
【0006】
【発明が解決しようとする課題】
本発明は、低温雰囲気下での出力とサイクル寿命とを高いレベルで両立させたリチウム二次電池を与える正極活物質複合化粒子、並びに該複合化粒子を用いた正極及びリチウム二次電池を提供することを課題とする。
【0007】
【課題を解決するための手段】
本発明者等は、上記課題を解決すべく鋭意検討した結果、(A)リチウム・ニッケル系複合酸化物、(B)活性炭及び(C)カーボンブラックからなる混合物に圧縮剪断応力を加える処理を施して製造される正極活物質複合化粒子を用いて作製したリチウム二次電池が、低温雰囲気下での出力とサイクル寿命とに優れていることを見出し、本発明に到達した。
【0008】
すなわち、本発明の要旨は、(A)リチウム・ニッケル系複合酸化物、(B)活性炭及び(C)カーボンブラックからなる混合物に圧縮剪断応力を加える処理を施して製造されることを特徴とするリチウム二次電池正極活物質複合化粒子に存する。
【0009】
【発明の実施の形態】
本発明に係る正極活物質複合化粒子を構成する(A)リチウム・ニッケル系複合酸化物は、リチウム及びニッケルのほかに、更に他の元素を含有していてもよい。この複合酸化物としては、基本組成がLiNiO2、Li2NiO2、LiNi2O4及びLi2Ni2O4等で表されるもの、並びにこれらのニッケルの一部を他の元素で置換したものが挙げられる。このうち、下記一般式(I)で表されるものが好ましい。
【0010】
【化2】
LiaNibMcO2 (I)
(式中、aは0.9以上1.2以下、bは0.5以上1.2以下、b+cは0.9以上1.2以下の数であり、MはBe、B、Mg、Al、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Cu、Zn及びGaよりなる群から選択される元素を示す。)
式(I)において、aが1.2を超え、かつb+cが0.9未満になると結晶のニッケルサイトをリチウムが多く交換するため、電池容量が低下してしまう。また、aが0.9未満であり、かつb+cが1.2以上となると、電池の充放電に関与できるリチウムが減少するため、電池容量が低下してしまう。したがって、aの上限としては1.1以下、特に1.05以下が好ましく、下限としては0.95以上が好ましい。また、b+cの下限としては0.95以上が好ましく、上限としては1.1以下、特に1.05以下が好ましい。bの下限としては0.5以上、特に0.55以上が好ましく、上限としては1.1以下、特に1.05以下が好ましい。なお、Mは必須成分ではないのでcは0であってもよく、上限としては0.6以下、特に0.5以下が好ましい。
【0011】
Mは、好ましくはB、Mg、Al、Ca、Cr、Mn、Fe及びCoよりなる群から選ばれた少なくとも1種の元素であるが、特にB、Al、Cr、Mn及びCoよりなる群から選ばれたものが好ましい。このうち、Al及び/又はCoが好ましく、Coが最も好ましい。
本発明において、(A)リチウム・ニッケル系複合酸化物としては、通常はSEM観察により測定した平均一次粒子径が0.01μm以上30μm以下のものを用いる。平均一次粒子径の下限は0.02μm以上、特に0.1μm以上が好ましく、上限は5μm以下、特に2μm以下が好ましい。
【0012】
また、レーザー回折/散乱式粒度分布測定装置により測定した平均二次粒子径(平均粒子径)は、通常は1μm以上50μm以下である。平均二次粒子径の下限は4μm以上が好ましく、上限は40μm以下、特に30μm以下が好ましい。
更に、BET式粉体比表面積測定装置を用い、ASTM D3037に準拠したBET法(窒素表面積法)により測定した比表面積は、通常は0.1m2/g以上10.0m2/g以下である。比表面積の上限は5.0m2/g以下、特に2.0m2/g以下が好ましく、下限は0.5m2/g以上が好ましい。
【0013】
(A)リチウム・ニッケル系複合酸化物は、リチウム源化合物及びニッケル源化合物、並びに所望の他の元素源化合物を配合し、乾式法又は湿式法により処理して、粉体として調製することができる。
好ましくは、水等の媒体に上記の各元素源化合物を加え媒体攪拌式粉砕機等の湿式粉砕機により粉砕・混合して調製したスラリー、又は乾式粉砕機により粉砕した各元素源化合物を水等の媒体中で混合して調製したスラリーを噴霧乾燥させた後、焼成する方法が挙げられる。なかでも湿式粉砕器で粉砕・混合する湿式法によるのが好ましい。
【0014】
湿式法において、スラリー中の固形分濃度は、通常10重量%以上50重量%以下である。10重量%未満では、噴霧乾燥処理で形成される粉体の粒子径が好ましい範囲に収まらない。また、50重量%を超えると、均一なスラリーを得ることができない。スラリー中の固形分濃度は、12.5重量%以上、35重量%以下とするのが好ましい。
【0015】
スラリー中の元素源化合物の平均粒子径は、レーザー回折/散乱式粒度分布測定装置により測定した値として、通常2μm以下0.01μm以上であるのが好ましい。2μmを超えると、焼成時の反応性が低くなり、高嵩密度のものを得ることができない。また、0.01μm未満にまで粉砕するのは、経済的ではない。平均粒子径の上限は1μm以下、特に0.5μm以下が好ましく、下限は0.05μm以上、特に0.1μm以上が好ましい。
【0016】
スラリーの粘度は、BM型粘度計により測定した値として、通常50mPa・秒以上3000mPa・秒以下である。50mPa・秒未満では、噴霧乾燥処理で形成される粉体粒子径が好ましい範囲に収まらない。3000mPa・秒を超えると、スラリーが取扱いづらくなる。粘度の下限は100mPa・秒以上、特に200mPa・秒以上が好ましく、上限は2000mPa・秒以下、特に1600mPa・秒以下が好ましい。
【0017】
リチウム・ニッケル系複合酸化物のリチウム源化合物又はニッケル源化合物としては、それぞれの金属の酸化物、水酸化物、炭酸塩、硝酸塩、硫酸塩、酢酸塩や蓚酸塩等のカルボン酸塩、アルキル化物及びハロゲン化物等が挙げられる。
リチウム源化合物としては、Li2O、LiOH、LiOH・H2O、Li2CO3 、LiNO3、LiOCOCH3、(LiOCO)2、LiCH3、LiC2H5、LiCl、LiI及びクエン酸リチウム等が挙げられる。このうち、LiOH・H2O、Li2CO3、LiNO3又はLiOCOCH3、特にLiOH・H2Oが好ましい。
【0018】
ニッケル源化合物としては、NiO、Ni(OH)2、NiOOH、NiCO3・2Ni(OH)2・4H2O、Ni(NO3)2・6H2O、NiSO4、NiSO4・6H2O、NiC2O4・2H2O、Ni(OCOCH3)2及びNiCl2等が挙げられる。このうち、NiO、Ni(OH)2、NiOOH、NiCO3・2Ni(OH)2・4H2O又はNiC2O4・2H2O、特にNiO、Ni(OH)2又はNiOOHが好ましい。
【0019】
(A)リチウム・ニッケル系複合酸化物に含まれていてもよい他の元素の原料化合物としては、それぞれの金属の酸化物、水酸化物、炭酸塩、硝酸塩、硫酸塩、タングステン酸塩、酢酸塩や蓚酸塩等のカルボン酸塩、アルキル化物、ハロゲン化物及び炭化物等が挙げられる。以下にそのいくつかを例示する。
マグネシウム源化合物としては、MgO、Mg(OH)2、Mg(NO3)2・6H2O、MgSO4、MgC2O4・2H2O、Mg(OCOCH3)2・4H2O及びMgCl2等が挙げられる。このうち、MgO又はMg(OH)2、特にMg(OH)2が好ましい。
【0020】
アルミニウム源化合物としては、Al2O3、Al(OH)3、AlOOH、Al(NO3)3・9H2O、Al2(SO4)3及びAlCl3等が挙げられる。このうち、Al2O3、Al(OH)3又はAlOOH、特にAlOOHが好ましい。
カルシウム源化合物としては、CaO、Ca(OH)2、CaCO3、Ca(NO3)2・4H2O、CaSO4・2H2O、CaC2O4・H2O、Ca(OCOCH3)2・H2O及びCaCl2等が挙げられる。このうち、CaO、Ca(OH)2又はCaCO3、特にCa(OH)2が好ましい。
【0021】
クロム源化合物としては、CrO、CrO2、Cr2O3、Cr(OH)2、Cr2O3・nH2O、CrSO4・7H2O、Cr2(SO4)3、Cr(OCOCH3)2・2H2O、Cr(OCOCH3)3、CrCl2及びCrCl3等が挙げられる。このうち、CrO、CrO2、Cr2O3、Cr(OH)2又はCr2O3・nH2O、特にCrO、CrO2又はCr2O3が特に好ましい。
【0022】
マンガン源化合物としては、MnO2、Mn2O3、Mn3O4、MnOOH、MnCO3、Mn(NO3)2、MnSO4、Mn(OCOCH3)2、Mn(OCOCH3)3、MnCl2、MnCi3及びクエン酸マンガン等が挙げられる。このうち、MnO2、Mn2O3、Mn3O4又はMnOOH、特にMnO2、Mn2O3又はMn3O4が好ましい。
【0023】
鉄源化合物としては、Fe2O3、Fe3O4、FeOOH、Fe(NO3)3・9H2O、FeSO4・7H2O、Fe2(SO4)3・nH2O、FeC2O4・2H2O、FeCl2及びFeCl3等が挙げられる。このうち、Fe2O3、Fe3O4又はFeOOH、特にFe2O3、FeOOHが好ましい。
コバルト源化合物としては、CoO、Co2O3、Co3O4、Co(OH)2、Co(NO3)2・6H2O、Co(SO4)2・7H2O、Co(OCOCH3)2・4H2O及びCoCl2等が挙げられる。このうち、CoO、Co2O3、Co3O4又はCo(OH)2、特にCo(OH)2が好ましい。
【0024】
スラリーの噴霧乾燥は、公知のいずれの方法でも行うことができる。好ましいのは、ノズルの先端から加圧気体を用いてスラリーを噴射させる方法である。ノズルとしては、任意のものを用いることができる。例えば、特許第2797080号公報に記載されているような中心と外周から加圧気体を噴射し、内周からリング状にスラリーを噴射する三重管構造のノズルが好ましい。この加圧気体としては、空気、窒素等が好ましい。ガス線速は、通常100m/秒以上1000m/秒以下である。200m/秒以上、特に300m/秒以上が好ましい。乾燥用ガスとしては、通常50℃以上120℃以下、好ましくは70℃以上100℃以下の加熱空気又は窒素等を、上部から下部に向けてダウンフローさせるのが好ましい。特に好ましいのは、ノズルからスラリーを水平方向に噴射させ、これに直行するように乾燥用ガスをダウンフローさせる方法である。
【0025】
噴霧乾燥により、球状の粉体が得られる。粉体の平均粒子径は、噴霧方法、ノズル形状、加圧気体噴射速度、スラリー供給速度及び加熱気体流温度等によって制御することができる。レーザー回折/散乱式粒度分布測定装置により測定した値として、通常は粒径が4μm以上50μm以下の粉体が得られるようにする。5μm以上30μm以下の粒径の粉体が得られるようにするのが好ましい。
【0026】
この粉体を箱型炉、管状炉、トンネル炉又はロータリーキルン等の装置内で、空気等の酸素含有ガス若しくは酸素ガス雰囲気下、又は窒素若しくはアルゴン等の不活性ガス雰囲気下、加熱することにより焼成し、リチウム・ニッケル系複合酸化物とする。酸素含有ガス又は酸素ガス雰囲気下で加熱するのが好ましい。
焼成は、通常700℃以上1050℃以下で行う。700℃未満では、複合酸化物への反応性が低下してしまう。一方、1050℃を超えると、複合酸化物の層状構造に欠陥が生じてしまう。焼成温度の下限は750℃以上、特に800℃以上が好ましく、上限は1000℃以下、特に950℃以下が好ましい。
【0027】
加熱時間としては、0.5〜50時間が好ましい。
加熱処理後は、5℃/分以下の速度で徐冷するのが好ましい。
(B)活性炭としては、任意のものを使用することができる。通常は平均粒子径が1μm以上30μm以下であるものを用いる。また、BET法による比表面積は、500m2/g以上3000m2/g以下であるものが好ましい。500m2/g未満では、電池の低温雰囲気下における出力の向上効果が低下し、一方、3000m2/gを超えると、正極活物質含有層の嵩密度が低下し、体積あたりの容量が低下する。比表面積の下限は600m2/g以上、特に800m2/g以上が好ましい。最も好ましいのは、1000m2/g以上である。上限は、2800m2/g以下、特に2600m2/g以下が好ましい。
【0028】
(C)カーボンブラックとしては、導電性を有するものであれば任意のものを用いることができる。単独で用いても、2種以上を併用してもよい。
カーボンブラックの平均粒子径は、一次粒子径として、通常1nm以上500nm以下のものを用いる。1nm未満では製造上の面から好ましくない。一方、500nmを超えると正極活物質含有組成物に導電性を付与しにくくなる。平均粒子径の下限としては5nm以上が好ましく、上限としては100nm以下が好ましい。
【0029】
カーボンブラックの具体例としては、市販されているアセチレンブラック、「ケッチェンブラック」(ケッチェンブラックインターナショナル社製)として市販されている特殊ファーネスブラック、及び「三菱導電性カーボンブラック」又は「三菱カーボンブラック」(三菱化学社製)として市販されているその他カーボンブラックなどが挙げられる。
【0030】
本発明に係る正極活物質複合化粒子は、上述の(A)リチウム・ニッケル系複合酸化物、(B)活性炭及び(C)カーボンブラックの各成分を含有する混合物に圧縮剪断応力を加える処理を行うことにより製造されるものである。
この混合物の組成としては、(A):75重量%以上99.8重量%以下、(B):0.1重量%以上15重量%以下、及び(C):0.1重量%以上10重量%以下が好ましい。
【0031】
(A)の下限としては82重量%以上、特に87重量%以上が好ましい。上限としては97重量%以下、特に95重量%以下が好ましい。
(B)が0.1重量%未満では、低温時の特性が低下する。一方、15重量%を超えると、体積あたりの電池容量が低下する。下限としては2重量%以上、特に3重量%以上が好ましい。上限としては12重量%以下、特に8重量%以下が好ましい。
【0032】
(C)が0.1重量%未満では、十分な出力向上効果が得られない。一方、10重量%を超えると、複合化粒子の抵抗が増加するため低温での出力を阻害する。下限としては1重量%以上、特に2重量%以上が好ましい。上限としては6重量%以下、特に5重量%以下が好ましい。
また、(B)と(C)とを合わせた炭素成分において、(B)が25重量%以上95重量%以下とするのが好ましい。(B)が25重量%未満では、低温特性の改善効果が低下する。一方、(B)が95重量%を超えると、高温サイクル寿命が低下する。(B)の下限としては40重量%以上、特に50重量%以上が好ましく、上限としては90重量%以下、特に80重量%以下が好ましい。
【0033】
圧縮剪断応力を加える処理とは、(A)、(B)及び(C)の各成分を所定の比率で配合したものに、特開平11−154515号公報や特開2000−123876号公報に記載されている方法と同じく、圧縮及び剪断応力を加える操作をいう。これにより圧縮された配合物は一体化されると共に、一体化したものの一部が剪断応力により削られて微粉となり、これが再び一体化された粒子に結合されるという、いわゆるメカノフュージョンが発現されるものと考えられる。この処理は、例えば、「メカノフュージョンンシステム」(ホソカワミクロン社製)、又は「ハイブリダイゼーションシステム」(奈良機械製作所社製)等を用いて行うことができる。
【0034】
上記のメカノフュージョン処理で得られたリチウム二次電池正極活物質複合化粒子に、(D)導電剤及び(E)結着剤を加えて混合することにより、リチウム二次電池正極活物質複合化粒子含有組成物を調製する。
(D)導電材としては、リチウム二次電池に用いられることが知られているいずれのものも用いることができる。例えば、カーボンブラック及び黒鉛等が挙げられる。
【0035】
(E)結着剤としては、リチウム二次電池に用いられることが知られているいずれのものも用いることができる。例えば、ポリビニリデンフルオライド、ポリテトラフルオロエチレン、ポリメチルメタクリレート及びポリエチレン等の樹脂;スチレンブタジエンゴム、アクリロニトリルブタジエンゴム、エチレンプロピレンゴム、フッ素ゴム等のゴム;ポリ酢酸ビニル及びセルロース等の高分子物質などが挙げられる。
【0036】
リチウム二次電池正極活物質複合化粒子含有組成物としては、複合化粒子を70重量%以上98.9重量%以下、(D)導電材を1重量%以上10重量%以下、(E)結着剤を0.1重量%以上20重量%以下で含有するものが好ましい。
複合化粒子が70重量%未満では、電池容量等の電池特性を十分に確保することが困難となる。一方、98.9重量%を超えると、電極としての機械的強度を確保することが困難となる。複合化粒子は75重量%以上、特に80重量%以上含有するのが好ましく、上限は97重量%以下、特に95重量%以下が好ましい。
【0037】
(D)導電剤が1重量%未満では良好なサイクル寿命を得ることが困難である。一方、10重量%を超えると体積電池容量が低下する。(D)の下限は2重量%以上、特に3重量%以上が好ましく、上限は10重量%以下、特に5重量%以下が好ましい。
(E)結着剤が0.1重量%未満では、電極としての機械的強度を確保することが困難である。一方、20重量%を超えると、電池容量や導電性等の電池特性を十分に確保することができない。(E)の下限は3重量%以上、特に5重量%以上が好ましく、上限は15重量%以下、特に10重量%以下が好ましい。
【0038】
なお、このリチウム二次電池正極活物質複合化粒子含有組成物中に、更にLiFePO4等のリチウムイオンを吸蔵・放出し得る他の正極活物質を含有させてもよい。
得られたリチウム二次電池正極活物質複合化粒子含有組成物を溶媒に分散させて調製した塗布液を、集電体表面に塗布し乾燥させた後、一軸プレスやロールプレス等による圧密化処理を行うことにより、集電体表面にリチウム二次電池正極活物質複合化粒子含有組成物からなる層を有するリチウム二次電池の正極を製造する。
【0039】
溶媒としては、エチレンオキシド及びテトラヒドロフラン等のエーテル系溶媒;メチルエチルケトン及びシクロヘキサノン等のケトン系溶媒;酢酸メチル及びアクリル酸メチル等のエステル系溶媒;ジエチルトリアミン及びN,N−ジメチルアミノプロピルアミン等のアミン系溶媒;N−メチルピロリドン、ジメチルホルムアミド及びジメチルアセトアミド等の非プロトン性極性溶媒;並びに水等が挙げられる。
【0040】
正極の集電体の材質としては、アルミニウム、ステンレス鋼、ニッケルメッキ鋼等が挙げられる。その厚みは、通常1〜1000μmである。5〜500μm、特に5〜100μmが好ましい。正極の集電体としては、アルミニウム箔が好ましい。
集電体表面のリチウム二次電池正極活物質複合化粒子含有組成物層は、通常厚みが1〜1000μmとなるように製造する。10〜200μmの厚みのものが好ましい。
【0041】
負極の製造は、常法によればよい。例えば、負極活物質を結着剤と共に溶媒に分散させて調製した塗布液を集電体表面に塗布し、乾燥させ、一軸プレスやロールプレス等による圧密化処理を行う方法が挙げられる。
負極活物質としては、リチウム、リチウムアルミニウム合金;黒鉛、石炭系又は石油系コークスの炭化物、石炭系又は石油系ピッチの炭化物、ニードルコークス、ピッチコークス、フェノール樹脂又は結晶セルロース等の炭化物、ファーネスブラック又はアセチレンブラック等のカーボンブラック;SnO、SnO2、Sn1−xM1 xO(式中、M1はHg、P、B、Si、Ge又はSbを表し、xは0<x<1の数を表す。)、Sn3O2(OH)2、Sn3−xM2 xO2(OH)2(式中、M2はMg、P、B、Si、Ge、Sb又はMnを表し、xは0<x<3の数を表す。)、LiSiO2、SiO2又はLiSnO2等が挙げられる。
【0042】
結着剤としては、リチウム二次電池に用いられることが知られているいずれのものも用いることができる。例えば、ポリビニリデンフルオライド、ポリテトラフルオロエチレン、ポリメチルメタクリレート及びポリエチレン等の樹脂;スチレンブタジエンゴム、アクリロニトリルブタジエンゴム、エチレンプロピレンゴム、弗素ゴム等のゴム;ポリ酢酸ビニル及びセルロース等の高分子物質などが挙げられる。
【0043】
溶媒としては、エチレンオキシド及びテトラヒドロフラン等のエーテル系溶媒;メチルエチルケトン及びシクロヘキサノン等のケトン系溶媒;酢酸メチル及びアクリル酸メチル等のエステル系溶媒;ジエチルトリアミン及びN,N−ジメチルアミノプロピルアミン等のアミン系溶媒;N−メチルピロリドン、ジメチルホルムアミド及びジメチルアセトアミド等の非プロトン性極性溶媒;並びに水等が挙げられる。
【0044】
負極の集電体の材質としては、銅、ニッケル、ステンレス鋼、ニッケルメッキ鋼等の箔が挙げられ、このうち銅箔が好ましい。
電解質としては、リチウム二次電池に用いられることが知られているいずれのものも用いることができる。例えば、有機電解液に用いられる電解質、高分子固体電解質、ゲル状電解質、無機固体電解質等が挙げられる。このうち有機電解液に用いられる電解質が好ましい。
【0045】
有機電解液に用いられる電解質としては、LiCl、LiBr、LiClO4、LiAsF6、LiPF6、LiBF4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiN(SO3CF3)2及びLiC(SO2CF3)3等が挙げられる。
【0046】
有機溶媒としては、ジエチルエーテル、1,2−ジメトキシエタン、1,2−ジエトキシエタン、テトラヒドロフラン、2−メチルテトラヒドロフラン、1,4−ジオキサン、1,3−ジオキソラン、4−メチル−1,3−ジオキソラン等のエーテル類;4−メチル−2−ペンタノン等のケトン類;メチルホルメート、メチルアセテート、メチルプロピオネート等の脂肪酸エステル類;ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ビニレンカーボネート等のカーボネート類;γ−ブチロラクトン、γ−バレロラクトン等のラクトン類;1,2−ジクロロエタン等のハロゲン化炭化水素類;スルホラン、メチルスルホラン等のスルホラン系化合物類;アセトニトリル、プロピオニトリル、ブチロニトリル、バレロニトリル、ベンゾニトリル等のニトリル類;ジエチルアミン、エチレンジアミン、トリエタノールアミン等のアミン類;リン酸トリメチル、リン酸トリエチル等のリン酸エステル類、N,N−ジメチルホルムアミド、N−メチルピロリドン、ジメチルスルホキシド等の非プロトン性極性溶媒などが挙げられる。
【0047】
これらのうち、25℃における比誘電率が20以上の高誘電率溶媒が好ましい。このような溶媒としては、エチレンカーボネート及びプロピレンカーボネート、並びにこれらの水素原子がハロゲン原子又はアルキル基等で置換された化合物が好ましい。有機溶媒全体に占める高誘電率溶媒の割合は、通常20重量%以上である。30重量%以上、特に40重量%以上とするのが好ましい。
【0048】
リチウム二次電池の正極と負極の間には、セパレータを介在させてもよい。セパレータとしては、ポリエチレン及びポリプロピレン等のポリオレフィン;ポリビニリデンフルオライド、ポリテトラフルオロエチレン、ポリエステル、ポリアミド、ポリスルホン、ポリアクリロニトリル、セルロース及びセルロースアセテート等の高分子の微多孔性フィルム;これらの高分子繊維やガラス繊維等の不織布フィルター等が挙げられる。これらのうち、ポリエチレン微多孔性フィルムが好ましい。ポリエチレンとしては、分子量50万以上500万以下のものが好ましい。50万未満では、高温での形状維持性を確保するのが困難となる。一方、500万を超えると、高温での微多孔の閉塞性を確保するのが困難となる。分子量の下限は100万以上、特に150万以上が好ましく、上限は400万以下、特に300万以下が好ましい。
【0049】
【実施例】
以下、本発明を実施例により更に具体的に説明するが、本発明はその要旨を超えない限り以下の実施例に限定されるものではない。
なお、以下の実施例及び比較例においては、(A)リチウム・ニッケル系複合酸化物、(B)活性炭、(C)カーボンブラック、(D)導電材、及び(E)結着剤は、以下のものを用いた。
【0050】
また、リチウム二次電池正極活物質複合化粒子は、メカノフュージョンシステム「AM−20FS」(ホソカワミクロン社製)を用い、回転数2600rpmで20分間圧縮剪断応力を加えることにより製造した。
(A)リチウム・ニッケル系複合酸化物
A−1:平均二次粒子径9μm、BET法による比表面積0.7m2/gのLi1.05Ni0.80Co0.15Al0.05O2で表される層状リチウム・ニッケル・コバルト・アルミニウム複合酸化物
A−2:平均二次粒子系7μm、BET法による比表面積0.5m2/gのLi1.05Ni0.80Co0.15Al0.05O2で表される層状リチウム・ニッケル・コバルト・アルミニウム複合酸化物。
【0051】
(B)活性炭
平均粒子径6μm、BET法による比表面積1000m2/gの活性炭。
(C)カーボンブラック
平均一次粒子系30nm、BET法による比表面積1280m2/gのケッチェンブラック(ケッチェンブラックインターナショナル社製)。
【0052】
(D)導電材
D−1:平均一次粒子系30nm、BET法による比表面積800m2/gのケッチェンブラック(ケッチェンブラックインターナショナル社製)
D−2:平均一次粒子径35nm、BET法による比表面積39m2/gのアセチレンブラック(電気化学工業社製)。
【0053】
(E)結着剤
ポリビニリデンフルオライド「PVDF#1100」(呉羽化学工業製)。
実施例1〜3、比較例1〜4
表1に示す組成で(A)、(B)及び(C)を用いてリチウム二次電池正極活物質複合化粒子を製造した。
【0054】
【表1】
【0055】
また、表2に示す組成で上記で得られた複合化粒子、(D)及び(E)を用いて、リチウム二次電池正極活物質複合化粒子含有組成物を製造した。
なお、比較例1は、(A)及び(C)の混合物に圧縮剪断応力を加える処理を施して得られたリチウム二次電池正極活物質複合化粒子に、(B)、(D)及び(E)を加えて製造したリチウム二次電池正極活物質複合化粒子含有組成物を用いた。
【0056】
【表2】
【0057】
各リチウム二次電池正極活物質複合化粒子含有組成物をN−メチル−2ピロリドンに分散して得られたスラリーを、厚さ20μmのアルミ箔の片面に塗布し乾燥させた後、直径12mm(12φ)の円形に打ち抜き、これをプレスして正極とした。正極中の活物質量は約13mgであった。
この正極塗布膜を9φに打ち抜いたものを試験極とし、Li金属を対極としてコインセルを組み、これに0.2mA/cm2の定電流で上限4.2V下限3.2Vで充放電する試験を実施し、正極活物質単位重量当たりの初期充電容量〔Qs(mAh/g)〕、初期放電容量〔Qd1(mAh/g)〕を測定した。
【0058】
また、平均粒子径8〜12μmの黒鉛粉末92.5重量部とポリビニリデンフルオライド「PVDF#1300」(呉羽化学工業製)7.5重量部とを、N−メチルピロリドンに分散させて調製したスラリーを厚さ20μmの銅箔の片面に塗布し、乾燥させた後、直径12mmの円形に打ち抜き、プレスして負極とした。
【0059】
この負極を試験極とし、リチウム金属を対極としてコインセルを組み、これに0.2mA/cm2の定電流で負極にリチウムイオンを吸蔵させる反応を下限0Vで行ったときの、負極活物質単位重量当たりの初期吸蔵容量〔Qf(mAh/g)〕を測定した。
正極缶の上に正極を載置し、その上にセパレータとして厚さ25μmの多孔性ポリエチレンフィルムを載置し、ポリプロピレン製ガスケットで押さえ、その上に負極を載置し、更に厚み調整用のスペーサーを載置した。これに、エチレンカーボネートとエチルメチルカーボネートの混合溶媒(容積比3:7)に六弗化燐酸リチウム(LiPF6)を1モル/リットルとなるように溶解させた電解液を加えて十分に滲み込ませた後、負極缶を載置し、封口することによりコインセルを作製した。なお、正極活物質重量/負極活物質重量={〔Qf(mAh/g)〕/1.2}/〔Qc(mAh/g)〕となるように設定した。
【0060】
コインセルについて、コンディショニング電流値〔I(mA)〕=〔Qd1(mAh/g)〕×正極活物質重量/5で、充電上限電圧4.1V、放電下限電圧3.0Vとして、充放電2サイクルの初期コンディショニングを行い、2サイクル目における正極活物質単位重量当たりの放電容量〔Qd2(mAh/g)〕を測定した。
【0061】
電池を十分緩和した後、1時間率電流値〔1C(mA)〕=〔Qd2(mAh/g)×正極活物質重量として、定電流1/(3C)で72分間充電を行い、1時間静置した。次いで、−30℃の低温雰囲気下で1時間以上静置した後、定電流2.5Cで4秒間放電を行った。このときの放電直前のOCV(Open Circuit Voltage)と放電4秒後のOCVとの差(ΔV)を測定することにより、クロノポテンショメトリーを測定した。結果を表2に示した。ΔVが小さい程、電池の抵抗が小さく大電力の取り出しが可能であり、低温雰囲気下での出力が向上していることを意味する。
【0062】
また、初期コンディショニング後のコインセルを、60℃雰囲気下で、定電流1C、充電上限電圧4.1V、放電下限電圧3.0Vとして、充放電を100サイクル繰り返した。引き続き0.2mAの充放電を2回繰り返し、サイクル後の容量を確認した。サイクル後2回目の放電容量をサイクル後のQd2としてクロノポテンショメトリーの測定を実施した。結果を表3に示した。
【0063】
【表3】
【0064】
【発明の効果】
本発明に係るリチウム二次電池正極活物質複合化粒子を含有する組成物を用いることにより、低温雰囲気下での出力及びサイクル寿命に優れたリチウム二次電池を作製することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to composite particles of a positive electrode active material used in a lithium secondary battery, and an electrode and a lithium secondary battery using the composite particles.
[0002]
[Prior art]
Lithium secondary batteries are excellent in energy density and output density, and can be reduced in size and weight. Therefore, lithium secondary batteries have shown rapid growth as power supplies for portable devices such as notebook computers, mobile phones, and handy video cameras. In addition, it has attracted attention as a power source for electric vehicles and load leveling of electric power.
[0003]
A positive electrode used in a lithium secondary battery is generally composed of a current collector and a positive electrode active material layer formed on the surface thereof and containing a positive electrode active material, a conductive agent and a binder. As the positive electrode active material, a composite oxide of lithium and a transition metal such as manganese, cobalt or nickel, such as a lithium-manganese composite oxide, a lithium-cobalt composite oxide, or a lithium-nickel composite oxide, has high performance battery characteristics. Is gaining attention. A lithium secondary battery using these lithium-based composite oxides has an advantage that a high voltage can be obtained and a high output can be obtained. Currently, studies are actively being conducted to improve the stability of composite oxides, increase the capacity of batteries, and improve battery characteristics at high temperatures.
[0004]
Japanese Patent Application Laid-Open No. H11-154515 discloses a lithium-based composite oxide, a first conductive agent that covers the surface of each particle of the composite oxide, and a first conductive material interposed between the particles of the composite oxide and having a specific surface area of the first conductive material. A positive electrode active material including a second conductive agent smaller than the agent is described.
Japanese Patent Application Laid-Open No. 2000-123876 discloses that, while mixing a lithium-based composite oxide, a conductive agent and a binder, a pressing force and a shearing stress are applied to bind the conductive agent to the surface of the lithium-based composite oxide. A method for producing a positive electrode material which is subjected to a composite treatment by adhering with an agent is described.
[0005]
However, according to studies by the present inventors, lithium secondary batteries using these lithium-based composite oxides, particularly lithium-nickel-based composite oxides, have a high capacity but have low output in a low-temperature atmosphere. The problem of lowering has been found to be inherent.
In secondary batteries, cycle life is always considered important.
[0006]
[Problems to be solved by the invention]
The present invention provides a positive electrode active material composite particle that provides a lithium secondary battery having a high level of both output under a low-temperature atmosphere and cycle life, and a positive electrode and a lithium secondary battery using the composite particle. The task is to
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have performed a process of applying a compressive shear stress to a mixture comprising (A) a lithium-nickel-based composite oxide, (B) activated carbon, and (C) carbon black. It has been found that a lithium secondary battery produced using the positive electrode active material composite particles produced as described above has excellent output and cycle life in a low-temperature atmosphere, and has reached the present invention.
[0008]
That is, the gist of the present invention is characterized by being produced by subjecting a mixture comprising (A) a lithium / nickel-based composite oxide, (B) activated carbon and (C) carbon black to a treatment of applying compressive shear stress. In the lithium secondary battery positive electrode active material composite particles.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The lithium-nickel composite oxide (A) constituting the positive electrode active material composite particles according to the present invention may further contain other elements in addition to lithium and nickel. The basic composition of this composite oxide is LiNiO2, Li2NiO2, LiNi2O4And Li2Ni2O4And those obtained by substituting a part of these nickels with other elements. Among them, those represented by the following general formula (I) are preferable.
[0010]
Embedded image
LiaNibMcO2(I)
(Where a is a number from 0.9 to 1.2, b is a number from 0.5 to 1.2, b + c is a number from 0.9 to 1.2, and M is Be, B, Mg, Al , Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, and Ga.)
In the formula (I), when a exceeds 1.2 and b + c is less than 0.9, lithium replaces a large amount of nickel sites in the crystal, so that the battery capacity decreases. On the other hand, if a is less than 0.9 and b + c is 1.2 or more, the amount of lithium that can participate in charging and discharging of the battery decreases, so that the battery capacity decreases. Therefore, the upper limit of a is preferably 1.1 or less, particularly 1.05 or less, and the lower limit is preferably 0.95 or more. The lower limit of b + c is preferably 0.95 or more, and the upper limit is 1.1 or less, particularly preferably 1.05 or less. The lower limit of b is preferably at least 0.5, particularly preferably at least 0.55, and the upper limit is preferably at most 1.1, particularly preferably at most 1.05. Since M is not an essential component, c may be 0, and the upper limit is preferably 0.6 or less, particularly preferably 0.5 or less.
[0011]
M is preferably at least one element selected from the group consisting of B, Mg, Al, Ca, Cr, Mn, Fe and Co, and particularly from the group consisting of B, Al, Cr, Mn and Co. Selected ones are preferred. Of these, Al and / or Co are preferred, and Co is most preferred.
In the present invention, (A) a lithium-nickel-based composite oxide having an average primary particle diameter of 0.01 μm or more and 30 μm or less usually measured by SEM observation is used. The lower limit of the average primary particle size is preferably at least 0.02 μm, particularly preferably at least 0.1 μm, and the upper limit is preferably at most 5 μm, particularly preferably at most 2 μm.
[0012]
The average secondary particle diameter (average particle diameter) measured by a laser diffraction / scattering particle size distribution analyzer is usually 1 μm or more and 50 μm or less. The lower limit of the average secondary particle diameter is preferably 4 μm or more, and the upper limit is 40 μm or less, particularly preferably 30 μm or less.
Further, the specific surface area measured by the BET method (nitrogen surface area method) based on ASTM D3037 using a BET type powder specific surface area measuring device is usually 0.1 m2/ G or more 10.0m2/ G or less. The upper limit of the specific surface area is 5.0m2/ G or less, especially 2.0 m2/ G or less, and the lower limit is 0.5 m2/ G or more is preferred.
[0013]
(A) The lithium-nickel-based composite oxide can be prepared as a powder by mixing a lithium source compound, a nickel source compound, and other desired element source compounds and treating the mixture by a dry method or a wet method. .
Preferably, a slurry prepared by adding each of the above-mentioned element source compounds to a medium such as water and pulverizing and mixing with a wet pulverizer such as a medium stirring type pulverizer, or each element source compound pulverized by a dry pulverizer with water or the like After spray-drying the slurry prepared by mixing in the medium described above, followed by baking. Among them, it is preferable to use a wet method of pulverizing and mixing with a wet pulverizer.
[0014]
In the wet method, the solid content concentration in the slurry is usually from 10% by weight to 50% by weight. If it is less than 10% by weight, the particle size of the powder formed by the spray drying treatment does not fall within the preferred range. If it exceeds 50% by weight, a uniform slurry cannot be obtained. The solid concentration in the slurry is preferably 12.5% by weight or more and 35% by weight or less.
[0015]
The average particle diameter of the element source compound in the slurry is usually preferably 2 μm or less and 0.01 μm or more as a value measured by a laser diffraction / scattering particle size distribution analyzer. If it exceeds 2 μm, the reactivity at the time of firing will be low, and a material having a high bulk density cannot be obtained. It is not economical to grind to less than 0.01 μm. The upper limit of the average particle size is preferably 1 μm or less, particularly preferably 0.5 μm or less, and the lower limit is preferably 0.05 μm or more, particularly preferably 0.1 μm or more.
[0016]
The viscosity of the slurry is usually 50 mPa · sec or more and 3000 mPa · sec or less as a value measured by a BM type viscometer. If it is less than 50 mPa · s, the particle diameter of the powder formed by the spray drying treatment does not fall within the preferred range. If it exceeds 3000 mPa · s, the slurry becomes difficult to handle. The lower limit of the viscosity is preferably 100 mPa · sec or more, particularly preferably 200 mPa · sec or more, and the upper limit is preferably 2000 mPa · sec or less, particularly preferably 1600 mPa · sec or less.
[0017]
Examples of the lithium source compound or nickel source compound of the lithium-nickel composite oxide include oxides, hydroxides, carbonates, nitrates, sulfates, carboxylate salts such as acetates and oxalates, and alkylated compounds of the respective metals. And halides.
As the lithium source compound, Li2O, LiOH, LiOH.H2O, Li2CO3, LiNO3, LiOCOCH3, (LiOCO)2, LiCH3, LiC2H5, LiCl, LiI and lithium citrate. Of these, LiOH-H2O, Li2CO3, LiNO3Or LiOCOCH3Especially LiOH ・ H2O is preferred.
[0018]
NiO, Ni (OH) as the nickel source compound2, NiOOH, NiCO3・ 2Ni (OH)2・ 4H2O, Ni (NO3)2・ 6H2O, NiSO4, NiSO4・ 6H2O, NiC2O4・ 2H2O, Ni (OCOCH3)2And NiCl2And the like. Of these, NiO, Ni (OH)2, NiOOH, NiCO3・ 2Ni (OH)2・ 4H2O or NiC2O4・ 2H2O, especially NiO, Ni (OH)2Alternatively, NiOOH is preferred.
[0019]
(A) The raw material compounds of other elements that may be contained in the lithium-nickel composite oxide include oxides, hydroxides, carbonates, nitrates, sulfates, tungstates, and acetates of the respective metals. Carboxylates such as salts and oxalates, alkylated compounds, halides, and carbides are exemplified. Some of them are exemplified below.
MgO, Mg (OH) as a magnesium source compound2, Mg (NO3)2・ 6H2O, MgSO4, MgC2O4・ 2H2O, Mg (OCOCH3)2・ 4H2O and MgCl2And the like. Among them, MgO or Mg (OH)2Especially Mg (OH)2Is preferred.
[0020]
As the aluminum source compound, Al2O3, Al (OH)3, AlOOH, Al (NO3)3・ 9H2O, Al2(SO4)3And AlCl3And the like. Of these, Al2O3, Al (OH)3Alternatively, AlOOH, particularly AlOOH, is preferred.
CaO, Ca (OH) as the calcium source compound2, CaCO3, Ca (NO3)2・ 4H2O, CaSO4・ 2H2O, CaC2O4・ H2O, Ca (OCOCH3)2・ H2O and CaCl2And the like. Of these, CaO, Ca (OH)2Or CaCO3Especially Ca (OH)2Is preferred.
[0021]
As the chromium source compound, CrO, CrO2, Cr2O3, Cr (OH)2, Cr2O3・ NH2O, CrSO4・ 7H2O, Cr2(SO4)3, Cr (OCOCH3)2・ 2H2O, Cr (OCOCH3)3, CrCl2And CrCl3And the like. Of these, CrO, CrO2, Cr2O3, Cr (OH)2Or Cr2O3・ NH2O, especially CrO, CrO2Or Cr2O3Is particularly preferred.
[0022]
As a manganese source compound, MnO2, Mn2O3, Mn3O4, MnOOH, MnCO3, Mn (NO3)2, MnSO4, Mn (OCOCH3)2, Mn (OCOCH3)3, MnCl2, MnCi3And manganese citrate. Of these, MnO2, Mn2O3, Mn3O4Or MnOOH, especially MnOOH2, Mn2O3Or Mn3O4Is preferred.
[0023]
Fe source compounds include Fe2O3, Fe3O4, FeOOH, Fe (NO3)3・ 9H2O, FeSO4・ 7H2O, Fe2(SO4)3・ NH2O, FeC2O4・ 2H2O, FeCl2And FeCl3And the like. Of these, Fe2O3, Fe3O4Or FeOOH, especially Fe2O3, FeOOH are preferred.
As the cobalt source compound, CoO, Co2O3, Co3O4, Co (OH)2, Co (NO3)2・ 6H2O, Co (SO4)2・ 7H2O, Co (OCOCH3)2・ 4H2O and CoCl2And the like. Of these, CoO, Co2O3, Co3O4Or Co (OH)2Especially Co (OH)2Is preferred.
[0024]
Spray drying of the slurry can be performed by any known method. A preferred method is to spray the slurry from the tip of the nozzle using a pressurized gas. Any nozzle can be used. For example, a nozzle having a triple tube structure that injects pressurized gas from the center and outer periphery and injects slurry in a ring shape from the inner periphery as described in Japanese Patent No. 2797080 is preferable. As the pressurized gas, air, nitrogen, or the like is preferable. The gas linear velocity is usually 100 m / sec or more and 1000 m / sec or less. It is preferably at least 200 m / sec, particularly preferably at least 300 m / sec. As the drying gas, it is preferable that heated air or nitrogen or the like having a temperature of usually 50 ° C. or more and 120 ° C. or less, preferably 70 ° C. or more and 100 ° C. or less be flowed downward from the upper portion to the lower portion. Particularly preferred is a method in which the slurry is jetted from the nozzle in the horizontal direction, and the drying gas is down-flowed so as to be perpendicular thereto.
[0025]
By spray drying, a spherical powder is obtained. The average particle diameter of the powder can be controlled by the spraying method, nozzle shape, pressurized gas injection speed, slurry supply speed, heated gas flow temperature, and the like. As a value measured by a laser diffraction / scattering type particle size distribution measuring device, usually, a powder having a particle size of 4 μm or more and 50 μm or less is obtained. It is preferable to obtain a powder having a particle size of 5 μm or more and 30 μm or less.
[0026]
This powder is fired in a box furnace, tubular furnace, tunnel furnace, rotary kiln, or other device by heating it under an oxygen-containing gas or oxygen gas atmosphere such as air or an inert gas atmosphere such as nitrogen or argon. To obtain a lithium-nickel-based composite oxide. The heating is preferably performed in an oxygen-containing gas or oxygen gas atmosphere.
The firing is usually performed at 700 ° C. or higher and 1050 ° C. or lower. If the temperature is lower than 700 ° C., the reactivity to the composite oxide is reduced. On the other hand, when the temperature exceeds 1050 ° C., defects occur in the layered structure of the composite oxide. The lower limit of the firing temperature is preferably 750 ° C or higher, particularly 800 ° C or higher, and the upper limit is preferably 1000 ° C or lower, particularly preferably 950 ° C or lower.
[0027]
The heating time is preferably 0.5 to 50 hours.
After the heat treatment, it is preferable to gradually cool at a rate of 5 ° C./min or less.
(B) Any activated carbon can be used. Usually, those having an average particle diameter of 1 μm or more and 30 μm or less are used. The specific surface area by the BET method is 500 m2/ G or more and 3000m2/ G or less is preferable. 500m2/ G, the effect of improving the output of the battery in a low-temperature atmosphere is reduced, while 3000 m2/ G, the bulk density of the positive electrode active material-containing layer decreases, and the capacity per volume decreases. The lower limit of the specific surface area is 600m2/ G or more, especially 800 m2/ G or more is preferred. Most preferred is 1000m2/ G or more. The upper limit is 2800m2/ G or less, especially 2600 m2/ G or less is preferred.
[0028]
(C) Any carbon black can be used as long as it has conductivity. They may be used alone or in combination of two or more.
The average particle diameter of the carbon black is usually from 1 nm to 500 nm as a primary particle diameter. If it is less than 1 nm, it is not preferable in terms of production. On the other hand, when it exceeds 500 nm, it becomes difficult to impart conductivity to the positive electrode active material-containing composition. The lower limit of the average particle diameter is preferably 5 nm or more, and the upper limit is preferably 100 nm or less.
[0029]
Specific examples of carbon black include commercially available acetylene black, special furnace black commercially available as “Ketjen Black” (manufactured by Ketjen Black International), and “Mitsubishi conductive carbon black” or “Mitsubishi carbon black”. "(Manufactured by Mitsubishi Chemical Corporation).
[0030]
The positive electrode active material composite particles according to the present invention are obtained by subjecting a mixture containing each of the components (A) to the lithium-nickel-based composite oxide, (B) to activated carbon and (C) to carbon black by applying a compressive shear stress. It is manufactured by performing.
As a composition of this mixture, (A): 75 to 99.8% by weight, (B): 0.1 to 15% by weight, and (C): 0.1 to 10% by weight. % Or less is preferable.
[0031]
The lower limit of (A) is preferably at least 82% by weight, particularly preferably at least 87% by weight. The upper limit is preferably 97% by weight or less, particularly preferably 95% by weight or less.
If (B) is less than 0.1% by weight, the characteristics at low temperatures are deteriorated. On the other hand, if it exceeds 15% by weight, the battery capacity per volume decreases. The lower limit is preferably 2% by weight or more, particularly preferably 3% by weight or more. The upper limit is preferably 12% by weight or less, particularly preferably 8% by weight or less.
[0032]
If (C) is less than 0.1% by weight, a sufficient output improving effect cannot be obtained. On the other hand, when the content exceeds 10% by weight, the resistance of the composite particles increases, which hinders the output at low temperatures. The lower limit is preferably 1% by weight or more, particularly preferably 2% by weight or more. The upper limit is preferably 6% by weight or less, particularly preferably 5% by weight or less.
In the carbon component obtained by combining (B) and (C), the content of (B) is preferably 25% by weight or more and 95% by weight or less. When (B) is less than 25% by weight, the effect of improving the low-temperature characteristics is reduced. On the other hand, when (B) exceeds 95% by weight, the high-temperature cycle life is reduced. The lower limit of (B) is preferably at least 40% by weight, particularly preferably at least 50% by weight, and the upper limit is preferably at most 90% by weight, particularly preferably at most 80% by weight.
[0033]
The process of applying a compressive shear stress is described in JP-A-11-154515 and JP-A-2000-123876, in which components (A), (B) and (C) are blended at a predetermined ratio. This means an operation of applying compressive and shear stress as in the case of the method. In this way, the compressed compound is integrated, and a part of the integrated material is shaved by shearing stress to become fine powder, which is bonded to the integrated particles again, so-called mechanofusion is exhibited. It is considered. This processing can be performed using, for example, "Mechano Fusion System" (manufactured by Hosokawa Micron), "Hybridization System" (manufactured by Nara Machinery Co., Ltd.), or the like.
[0034]
A lithium secondary battery positive electrode active material composite is obtained by adding (D) a conductive agent and (E) a binder to the lithium secondary battery positive electrode active material composite particles obtained by the above mechanofusion treatment and mixing them. A particle-containing composition is prepared.
(D) As the conductive material, any material known to be used for a lithium secondary battery can be used. Examples include carbon black and graphite.
[0035]
As the binder (E), any of those known to be used in lithium secondary batteries can be used. For example, resins such as polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate and polyethylene; rubbers such as styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, and fluoro rubber; polymer substances such as polyvinyl acetate and cellulose Is mentioned.
[0036]
As the composition containing the composite particles of the positive electrode active material for a lithium secondary battery, 70% by weight or more and 98.9% by weight or less of the composite particles, (D) 1% by weight or more and 10% by weight or less of the conductive material, and (E) Those containing 0.1% by weight or more and 20% by weight or less of the adhesive are preferred.
When the composite particles are less than 70% by weight, it is difficult to sufficiently secure battery characteristics such as battery capacity. On the other hand, if it exceeds 98.9% by weight, it is difficult to secure the mechanical strength as an electrode. The composite particles preferably contain at least 75% by weight, particularly at least 80% by weight, and the upper limit is at most 97% by weight, particularly preferably at most 95% by weight.
[0037]
(D) If the amount of the conductive agent is less than 1% by weight, it is difficult to obtain a good cycle life. On the other hand, if it exceeds 10% by weight, the volume battery capacity decreases. The lower limit of (D) is preferably at least 2% by weight, particularly preferably at least 3% by weight, and the upper limit is preferably at most 10% by weight, particularly preferably at most 5% by weight.
(E) When the amount of the binder is less than 0.1% by weight, it is difficult to secure the mechanical strength as an electrode. On the other hand, if it exceeds 20% by weight, battery characteristics such as battery capacity and conductivity cannot be sufficiently ensured. The lower limit of (E) is preferably at least 3% by weight, particularly preferably at least 5% by weight, and the upper limit is preferably at most 15% by weight, particularly preferably at most 10% by weight.
[0038]
It should be noted that LiFePO 4 was further added to the lithium secondary battery positive electrode active material composite particle-containing composition.4And other positive electrode active materials capable of inserting and extracting lithium ions.
A coating solution prepared by dispersing the obtained lithium secondary battery positive electrode active material composite particle-containing composition in a solvent is applied to the surface of the current collector, dried, and then subjected to a consolidation treatment using a uniaxial press or a roll press. Is carried out to produce a positive electrode of a lithium secondary battery having a layer made of the composition containing the composite particles of a positive electrode active material for a lithium secondary battery on the surface of the current collector.
[0039]
Examples of the solvent include ether solvents such as ethylene oxide and tetrahydrofuran; ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as methyl acetate and methyl acrylate; amine solvents such as diethyltriamine and N, N-dimethylaminopropylamine. Aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; and water.
[0040]
Examples of the material of the current collector of the positive electrode include aluminum, stainless steel, nickel-plated steel, and the like. Its thickness is usually 1 to 1000 μm. It is preferably from 5 to 500 μm, particularly preferably from 5 to 100 μm. As the current collector of the positive electrode, an aluminum foil is preferable.
The composition layer containing the lithium secondary battery positive electrode active material composite particles on the surface of the current collector is usually manufactured to have a thickness of 1 to 1000 μm. Those having a thickness of 10 to 200 μm are preferred.
[0041]
The production of the negative electrode may be performed according to a conventional method. For example, there is a method in which a coating solution prepared by dispersing a negative electrode active material in a solvent together with a binder is applied to the surface of the current collector, dried, and subjected to a consolidation treatment by a uniaxial press, a roll press, or the like.
As the negative electrode active material, lithium, lithium aluminum alloy; graphite, coal-based or petroleum-based coke carbide, coal-based or petroleum-based pitch carbide, needle coke, pitch coke, carbide such as phenolic resin or crystalline cellulose, furnace black or Carbon black such as acetylene black; SnO, SnO2, Sn1-xM1 xO (where M1Represents Hg, P, B, Si, Ge or Sb, and x represents a number satisfying 0 <x <1. ), Sn3O2(OH)2, Sn3-xM2 xO2(OH)2(Where M2Represents Mg, P, B, Si, Ge, Sb or Mn, and x represents a number satisfying 0 <x <3. ), LiSiO2, SiO2Or LiSnO2And the like.
[0042]
As the binder, any of those known to be used in lithium secondary batteries can be used. For example, resins such as polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate and polyethylene; rubbers such as styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, and fluoro rubber; high molecular substances such as polyvinyl acetate and cellulose Is mentioned.
[0043]
Examples of the solvent include ether solvents such as ethylene oxide and tetrahydrofuran; ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as methyl acetate and methyl acrylate; amine solvents such as diethyltriamine and N, N-dimethylaminopropylamine. Aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; and water.
[0044]
Examples of the material of the current collector of the negative electrode include foils of copper, nickel, stainless steel, nickel-plated steel, and the like, and among them, copper foil is preferable.
As the electrolyte, any of those known to be used for lithium secondary batteries can be used. For example, an electrolyte used for an organic electrolyte, a solid polymer electrolyte, a gel electrolyte, an inorganic solid electrolyte, and the like can be mentioned. Among them, the electrolyte used for the organic electrolyte is preferable.
[0045]
Examples of the electrolyte used for the organic electrolyte include LiCl, LiBr, and LiClO.4, LiAsF6, LiPF6, LiBF4, LiB (C6H5)4, LiCH3SO3, LiCF3SO3, LiN (SO2CF3)2, LiN (SO2C2F5)2, LiN (SO3CF3)2And LiC (SO2CF3)3And the like.
[0046]
Examples of the organic solvent include diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolan, and 4-methyl-1,3- Ethers such as dioxolane; ketones such as 4-methyl-2-pentanone; fatty acid esters such as methyl formate, methyl acetate, methyl propionate; dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate , Butylene carbonate, vinylene carbonate and other carbonates; lactones such as γ-butyrolactone and γ-valerolactone; halogenated hydrocarbons such as 1,2-dichloroethane; sulfolane such as sulfolane and methylsulfolane Nitriles such as acetonitrile, propionitrile, butyronitrile, valeronitrile and benzonitrile; amines such as diethylamine, ethylenediamine and triethanolamine; phosphates such as trimethyl phosphate and triethyl phosphate; Aprotic polar solvents such as N-dimethylformamide, N-methylpyrrolidone, and dimethylsulfoxide;
[0047]
Among these, a high dielectric constant solvent having a relative dielectric constant of 20 or more at 25 ° C. is preferable. As such a solvent, ethylene carbonate and propylene carbonate, and a compound in which a hydrogen atom thereof is substituted with a halogen atom, an alkyl group or the like are preferable. The proportion of the high dielectric constant solvent in the whole organic solvent is usually 20% by weight or more. It is preferably at least 30% by weight, particularly preferably at least 40% by weight.
[0048]
A separator may be interposed between the positive electrode and the negative electrode of the lithium secondary battery. As the separator, a polyolefin such as polyethylene and polypropylene; a microporous film of a polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyester, polyamide, polysulfone, polyacrylonitrile, cellulose and cellulose acetate; Non-woven fabric filters such as glass fiber are exemplified. Of these, polyethylene microporous films are preferred. Polyethylene having a molecular weight of 500,000 or more and 5,000,000 or less is preferable. If it is less than 500,000, it is difficult to maintain shape retention at high temperatures. On the other hand, when the amount exceeds 5,000,000, it becomes difficult to secure microporous obstruction at a high temperature. The lower limit of the molecular weight is preferably 1,000,000 or more, particularly preferably 1.5,000,000 or more, and the upper limit is preferably 4,000,000 or less, particularly preferably 3,000,000 or less.
[0049]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples as long as the gist is not exceeded.
In the following Examples and Comparative Examples, (A) lithium / nickel based composite oxide, (B) activated carbon, (C) carbon black, (D) conductive material, and (E) binder were as follows: Was used.
[0050]
The lithium secondary battery positive electrode active material composite particles were produced by applying a compressive shear stress for 20 minutes at a rotation speed of 2600 rpm using a mechanofusion system “AM-20FS” (manufactured by Hosokawa Micron Corporation).
(A) Lithium nickel composite oxide
A-1: average secondary particle diameter 9 μm, specific surface area 0.7 m by BET method2/ G Li1.05Ni0.80Co0.15Al0.05O2Lithium-nickel-cobalt-aluminum composite oxide represented by
A-2: average secondary particle system 7 μm, specific surface area 0.5 m by BET method2/ G Li1.05Ni0.80Co0.15Al0.05O2A layered lithium-nickel-cobalt-aluminum composite oxide represented by the formula:
[0051]
(B) Activated carbon
Average particle size 6μm, specific surface area 1000m by BET method2/ G of activated carbon.
(C) Carbon black
Average primary particle system 30nm, BET specific surface area 1280m2/ G Ketjen Black (Ketjen Black International).
[0052]
(D) Conductive material
D-1: average primary particle system 30 nm, specific surface area 800 m by BET method2/ G Ketjen Black (Ketjen Black International)
D-2: average primary particle diameter 35 nm, specific surface area 39 m by BET method2/ G of acetylene black (manufactured by Denki Kagaku Kogyo KK).
[0053]
(E) Binder
Polyvinylidene fluoride “PVDF # 1100” (manufactured by Kureha Chemical Industry).
Examples 1-3, Comparative Examples 1-4
Using the compositions shown in Table 1, (A), (B) and (C) were used to produce lithium secondary battery cathode active material composite particles.
[0054]
[Table 1]
[0055]
Further, using the composite particles (D) and (E) obtained above with the compositions shown in Table 2, a composition containing lithium secondary battery positive electrode active material composite particles was produced.
In Comparative Example 1, the lithium secondary battery positive electrode active material composite particles obtained by subjecting the mixture of (A) and (C) to a process of applying compressive shear stress include (B), (D), and ( The composition containing particles of the lithium secondary battery positive electrode active material composite prepared by adding E) was used.
[0056]
[Table 2]
[0057]
A slurry obtained by dispersing each lithium secondary battery positive electrode active material composite particle-containing composition in N-methyl-2-pyrrolidone was applied to one surface of a 20-μm-thick aluminum foil, dried, and then 12 mm in diameter ( (12φ) was punched out and pressed to obtain a positive electrode. The amount of active material in the positive electrode was about 13 mg.
The positive electrode coating film punched out to 9φ was used as a test electrode, and a coin cell was assembled using Li metal as a counter electrode.2A charge / discharge test was performed at an upper limit of 4.2 V and a lower limit of 3.2 V at a constant current of, and the initial charge capacity per unit weight of the positive electrode active material [Qs (mAh / g)] and the initial discharge capacity [Qd1 (mAh / g)] ] Was measured.
[0058]
Further, 92.5 parts by weight of graphite powder having an average particle size of 8 to 12 μm and 7.5 parts by weight of polyvinylidene fluoride “PVDF # 1300” (manufactured by Kureha Chemical Industry) were dispersed in N-methylpyrrolidone. The slurry was applied to one side of a copper foil having a thickness of 20 μm, dried, punched into a circular shape having a diameter of 12 mm, and pressed to obtain a negative electrode.
[0059]
This negative electrode was used as a test electrode, and a coin cell was assembled using lithium metal as a counter electrode.2The initial storage capacity [Qf (mAh / g)] per unit weight of the negative electrode active material was measured when the reaction for storing lithium ions in the negative electrode at a constant current of 0 V was performed at a lower limit of 0 V.
A positive electrode is placed on the positive electrode can, a 25 μm-thick porous polyethylene film is placed thereon as a separator, pressed with a polypropylene gasket, the negative electrode is placed thereon, and a spacer for thickness adjustment is further placed. Was placed. In addition, a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio of 3: 7) was mixed with lithium hexafluorophosphate (LiPF).6) Was added so as to have a concentration of 1 mol / liter, and the resulting mixture was sufficiently immersed. Then, a negative electrode can was placed and sealed to prepare a coin cell. The weight of the positive electrode active material / the weight of the negative electrode active material = {[Qf (mAh / g)] / 1.2} / [Qc (mAh / g)].
[0060]
With respect to the coin cell, the conditioning current value [I (mA)] = [Qd1 (mAh / g)] × the weight of the positive electrode active material / 5, the charge upper limit voltage of 4.1 V and the discharge lower limit voltage of 3.0 V, and two cycles of charge / discharge. Initial conditioning was performed, and the discharge capacity [Qd2 (mAh / g)] per unit weight of the positive electrode active material in the second cycle was measured.
[0061]
After the battery was sufficiently relaxed, the battery was charged for 72 minutes at a constant current of 1 / (3C), where 1 hour rate current value [1C (mA)] = [Qd2 (mAh / g) × weight of positive electrode active material, Was placed. Next, after leaving still in a low temperature atmosphere of -30 ° C for 1 hour or more, discharging was performed at a constant current of 2.5C for 4 seconds. Chronopotentiometry was measured by measuring the difference (ΔV) between the OCV immediately before the discharge (Open Circuit Circuit Voltage) and the OCV 4 seconds after the discharge. The results are shown in Table 2. The smaller the ΔV, the smaller the resistance of the battery, the more power can be taken out, and the higher the output under a low-temperature atmosphere.
[0062]
Further, the coin cell after the initial conditioning was charged and discharged 100 cycles at a constant current of 1 C, a charge upper limit voltage of 4.1 V, and a discharge lower limit voltage of 3.0 V in a 60 ° C. atmosphere. Subsequently, the charge / discharge of 0.2 mA was repeated twice, and the capacity after the cycle was confirmed. Chronopotentiometry was measured using the second discharge capacity after the cycle as Qd2 after the cycle. The results are shown in Table 3.
[0063]
[Table 3]
[0064]
【The invention's effect】
By using the composition containing the lithium secondary battery positive electrode active material composite particles according to the present invention, a lithium secondary battery having excellent output and cycle life under a low-temperature atmosphere can be manufactured.
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